I think TikTok has a case here, but I don’t think that angle is it. Otherwise, any business blocked by the US due to alleged crimes/embargoes/refusing to meet regulations can claim it is a violation of their right to free speech if they so much as maintain a website, notice board, or wall that Americans can stick flyers onto.

Any legal visitors/businesses/organizations etc. from abroad that enter or work in the United States are still protected by the bill of rights, so TikTok can claim this as a personal infringement despite being incorporated abroad.